Its ok when cut with bladed tools, mill/ lathe/saw but you are quite right its not good. The laser however causes causes the release of HCL which is carcinogenic and highly corrosive to anything it touches (I witnessed this in a cleanroom I was having built for a medical device). Cutting PVC with a laser is a very bad idea.

It is NOT safe to cut PVC with a laser. Be very careful and do your research before cutting plastics with lasers.Polyvinyl chloride (PVC) is a plasticizer that is used to make a multiplicity of products including signage, figurines, flooring and many other products.PVC emits extremely toxic and corrosive hydrogen chloride acid gas, dioxin, ethylene dichloride and vinyl chloride, which make a very toxic carcinogenic combination.Source:https://electrocorpairpurification.wordpress.com/2011/07/05/health-and-safety-concerns-laser-engraving-hazards/